The Mooney has a design problem regarding the sealant on the fuel tanks. If the tanks are not kept constantly full, then the sealant dries out and fuel seeping starts. But to get more than 1.5 full-size people and bags in the airplane, weight and balance demands that the pilot only fill the tanks to the tabs (leaving the tops of the tanks dry.) Fuel to the tabs is essentially never an operational problem because at 9 gph, that's 5.5 hours of fuel (or more conservatively 5 hours at 10 gph.) That's a lot of sitting and in a J-model Money a four-hour range can easily get you to Boston, Orlando/Tampa, or to the Chicago area (unless you're blasting into a serious headwind.)
But because we routinely fuel to the tabs, the sealant dries out and fuel starts to seep on the top of the wing when the tanks are filled past the tabs to the very tops. This creates a mess and might be a concern to a passenger looking out the window who does not realize that an external fuel stain or seep is permitted (in the maintenance manual) and is not unsafe.
But pilots new to the Mooney do not know this fact and have to be continuously educated about fueling procedures. (We had a flight canceled today for this reason.) Re-sealing the tanks generally takes two weeks or more of labor and can cost upwards of $6,000. So to help out, please remember to only have the Mooney tanks filled to the tabs! Thanks.
